Three million phenytoin-treated epileptic Americans manifest some degree of gingival overgrowth. Four new drugs also have this side effect (cyclosporine-A, nifedipine, valproic acid, felodipine). It is estimated that 30-35 million persons will be taking such drugs within the coming decade. The pathogenesis of drug-induced gingival overgrowth must be elucidated in order to establish preventive and/or therapeutic strategies. An increase in the dimension of the connective tissue component is always observed in the gingival lesions. Cell culture studies have shown that the most likely mechanism is in vivo selection of phenotypically stable subpopulations of fibroblasts characterized by elevated collagen and glycosaminoglycan synthesis, and by secretion of an inactive collagenase. The broad aim of the proposed studies is to elucidate further the roles of phenytoin metabolites, fibroblast subpopulation selection, genetic predisposition, marginal inflammation and specific microorganisms in the pathogenesis of phenytoin-induced gingival overgrowth in man and a mongrel cat model system. We will determine the effect of 3 major phenytoin metabolites on culture human and feline gingival fibroblasts. We shall also derive single-cell clones from mixed parent populations of cells, perform interclone comparisons of synthetic parameters, growth characteristics, cell size distributions, and phenytoin response in vitro, and examine selected clones ultrastructurally to detect clonal heterogeneity. Experiments will be performed to ascertain the chemical nature of the glycosaminoglycans that are produced in excess by phenytoin-sensitive subpopulations of cells. A study of gingival cells from human twins will be undertaken to determine if the phenytoin "responder" phenotype is, indeed, inherited as a genetic Mendelian recessive trait. The cat breeding study will continue to enhance the human twin experiments. Cytogenetic analyses (e.g., chromosome breakage, sister chromatid exchange) will be performed on fibroblasts from overgrown gingiva, with and without in vitro exposure to the drug. The additional and related phenytoid side effect, osteomalacca, will be studied in vitro using an osteoblast system to evaluate drug inhibition of bone metabolism. Knowledge gained from the proposed experiments should provide the rationale for development of novel prophylactic and therapeutic approaches in the control of gingival enlargement as well as similar and clinically more significant fibrotic-hyperplastic connective tissue lesions such as burn scar, keloid, arthritis, scleroderma, epidermolysis bullosa, systemic lupus erythematosis. New concepts in wound healing may also evolve.